This invention relates to an image converter method and apparatus for imaging of energetic radiation which term is used herein to include soft x-ray, gamma-ray and ultraviolet electromagnetic radiation, ions, electrons, photons and high energy particles.
It is known that two dimensional position and intensity distributions of incident energetic radiation can be determined by converting the incident radiation into an amplified burst of electrons and determining the position at which this burst of electrons strikes an anode or target element. Position determination can be performed by ratioing the charge collected at selected locations, such as four corners, on the anode or target, or by measuring the arrival time of the partitioned charges at these locations. The anode or target can either be a uniform resistive film or a regularly spaced geometric pattern of conducting wedges and strips.
A resistive anode image converter or encoder employing an optically opaque, carbonaceous anode film is described in U.S. Pat. No. 3,965,354 to M. L. Lampton and F. Paresce issued in the name of NASA and in an article Rev. Sci. Instrum. 45 (9), 1098 (1974). A low distortion anode fabricated using unspecified thick film resistor techniques was described by M. Lampton and C. W. Carlson in Rev. Sci. Instrum. 50 (9), 1093 (1979). A commercial resistive anode encoder product utilizing a thick film resistor anode and charge ratio detection circuitry was introduced in 1979 by Surface Science Laboratories, in Mountain View, California. The wedge and strip anodes are described in the articles by C. Martin, P. Jelinsky, M. Lampton and R. F. Malina Rev. Sci. Instrum 52 (7), 1067 (1981) and O. H. W. Siegmund, R. F. Malina, K. Coburn, and D. Werthimer, IEEE Transactions On Nuclear Science, Vol. NS-31, 1, 776 (1984).
The resistive anode image converter described in U.S. Pat. No. 3,965,354 to NASA includes two cascaded microchannel electron multiplier plates which both detect and amplify soft x-rays and ultraviolet electromagnetic radiation and charged particles which impinge upon the front surface of the first microchannel electron multiplier plate. A contiguously mounted continuous resistive anode which functions as a target for the amplified electron image produced by the microchannel multiplier plates is provided with a pulse position analysis circuit for producing electrical signals which represent the spatial coordinates of the points of impact of the electrons, which comprise the electron image, upon the resistive anode. U.S. Pat. No. 4,345,153 in the name of L. I. Yin and also issued to NASA discloses a spectrometer for imaging, counting and energy resolving employing alternative embodiments which use either a visible light output or a position sensing anode such as a resistive anode, cross grid anode or quadrant anode but not both. The resistive anode encoder and the visible light output devices suffer from the lack of both a quantitative resistive anode and a visual or qualitative indication of the position and intensity of the radiation incident on the microchannel plate assembly.